As a chemical reaction driven power source, such as a battery, is used, the reactants within the power source are consumed. Over time, the performance of the power source decreases, and the power source will eventually need to be recharged or replaced. For many surgically implanted medical devices, replacement of a drained power source may expose a person to risks associated with surgery. For example, to replace a power source in a pacemaker or similar implanted device, the device containing the power source often needs to be surgically removed, and a new device with a new power source inserted.
In general, despite surgical risks, it is desired to replace an implanted medical device in advance of significant depletion of its power source. More particularly, it is generally desired to replace an implanted medical device in advance of changes in device performance due to depletion of the power source. Implanted medical devices often provide a warning or other notification to the patient and/or a clinician so that a surgical procedure to replace the implanted device may be scheduled and completed in advance of changes in device performance due to depletion of the device power source. The warning or notification is sometimes referred to as, or provided via, an elective replacement indicator (ERI). The time at which such warnings or other notification are provided has sometimes been referred to as the recommended replacement time (RRT).
In general, implanted medical devices provide such warnings or indications of power source depletion upon the occurrence of a predetermined condition. More particularly, implanted medical devices generally monitor one or more parameters of the power source or the implanted medical device, such as battery voltage or impedance, and compare values of the parameters to one or more predetermined thresholds to determine when to provide the warning or indication of power source depletion. The threshold is typically a predetermined value that is common for every implanted medical device of a particular model, and selected such that the indication or warning is provided early enough to avoid degradation of device performance due to power source depletion in most circumstances, e.g., for most rates of power source depletion.